This invention relates to a method and apparatus for fabricating a tire by pressing a breaker and a tread radially inward against an outer circumferential surface of an annular carcass while adhering these with one another.
Generally, the process for fabricating a radial tire includes compressively adhering a carcass, a breaker, and a tread to one another (i.e., the stitching process). Conventionally, the stitching process has been carried out as follows. As shown in FIGS. 9 and 10, a component assembly d including the carcass a, the breaker b, and the tread c is mounted on a drum e. The component assembly d is rotated together with the drum e while filling the carcass a of the component assembly d with at a specified pressure through the drum e. At the same time, a stitch roller member h including a pair of rotatable rollers f is pressed against the outer circumferential surface of the tread c using a cylinder g. The carcass a, the breaker b, and the tread c are stitched by moving the rollers f from a center of the outer circumferential surface of the tread c to opposite ends thereof. In other words, the rollers f are moved away from each other as indicated by the phantom lines f in FIG. 10.
The adhering state of the tire after the stitching operation depends upon the magnitude of the pressing force applied by the stitch roller member to the outer circumferential surface of the tread c, the pressing time during which this pressing force is applied, and the like. Further, centrifugal force acts due to the rotation of the component assembly d during this adhering operation. Accordingly, it is necessary to set the pressure of the cylinder g, the internal pressure and rotating speed of the component assembly d, the pressing time, and the like according to the shape, thickness, and compounds of the tread c in consideration of the centrifugal force in order to obtain the satisfactory adhering state.
Specifically, in order to carry out a suitable stitching operation, it is generally preferable to increase the pressing force of the stitch roller member h by increasing the pressure of the cylinder g and the internal pressure of the component assembly d. However, if the pressing force is set at a high value, a portion of the component assembly d in contact with the stitch roller member h is suspectable to deformation. This may cause an inferior rubber flow at the time of vulcanization and poor appearance due to flaws. Further, an excessive pressing force causes a partial slip at a turned-up portion of a carcass ply, causing variations in the circumferential cord path (the length of a path extending from one turned-up portion to the other along the carcass ply. This may damage the dynamic uniformity of the tire.
At the same time, it is desirable to attain a sufficiently long pressing time of applying the pressing force in order to carry out the stitching operation properly. The longer the pressing time, the longer a cycle time required to fabricate one tire. This hinders improved productivity.